This is a proposal to continue ongoing studies to describe the structures of rat brain mRNAs, identify and characterize their protein products and characterize cis acting elements which may regulate their expression. 1) We will continue our characterization of the 1B236/MAG gene products. These studies will include refining structural information about the relationship between 1B236 and myelin- associated glycoprotein (MAG), investigation of the cell types in which particular alternatively spliced RNA products are formed, assignment of the membrane orientation of the 1B236/MAG protein, and search for an endogenous ligand for this protein which shares sequence identities and domain structures with immunoglobulin-type receptor molecules. 2) We will further study the distribution and transcription during development by Pol II and Pol III of ID elements, and isolate and characterize the mouse and monkey ID analogues. 3) We will study the enhancer properties of ID elements in neuronal and kidney cell cultures. 4) We will study the relationship between ID enhancer phenotypes and Pol III template activity by saturation point mutagenesis. 5) We will isolate full-length cDNA clones of rat mRNAs exclusive to or highly enriched in the brain compared to liver and kidney that exhibit regional differences in their concentration within brain, cross hybridize to analogous mouse and monkey brain mRNAs, and have postnatal developmental onset of expression. 6) We will determine the nucleotide sequences, map the 5' ends and investigate alternative forms of these mRNAs and then use the amino acid sequences deduced from their open reading frames to conduct computer searches and synthesize homologous peptides and fusion proteins. Antisera to these peptides will be used to describe the biochemical features and anatomical locations of the protein. 7) We will measure the relative portion of brain mRNA whose expression has postnatal onset.